1. Field of the Invention
The present invention is directed to a method for prescribed, structured deposition of micro-structures with laser light, and in particular to such a method wherein the prescribed substrate surface is previously coated with a thin metal film.
2. Description of the Prior Art
Laser-induced deposition from the adsorbed phase, from the vapor phase and from the liquid phase has been known for some time. In this method, the substrate to be structured is introduced into a reactive atmosphere and a chemical reaction is initiated using laser light. The deposition mechanism can be based on a photo-thermic or photo-chemical activation of the chemical reaction. In photo-thermic deposition, the reaction rates that are achieved are generally a few percentages higher than the reaction rates in photo-chemical deposition. The reaction rates in photo-thermic deposition are generally a few percentages higher because far higher concentrations of the reactive species can be employed in the photo-thermic deposition. For producing micro-structures by direct writing with the laser beam, continuous-wave (cw) ion lasers are particularly suitable. Additionally, on the basis of projection of the laser light, excimer lasers are especially suitable. From the vapor phase, particular interest in the photo-thermic deposition results. This is what is known as the pyrolytic LCVD process.
Chemical deposition from the vapor phase (LCVD method) induced by laser light is also described in "Chemical Processing with Lasers", Springer Series in Materials Science, Volume 1; "Materials Letters", Vol. 2 (1984), pages 263 through 264; EP published application No. 0182377; "Appl. Phys. Letters" 43 (1983) pages 454 through 456.
Japanese Published Application No. 53-39274 discloses that Al.sub.2 O.sub.3 be volatilized with laser emission in a vacuum from a source, or target, for this material. Further, the Al.sub.2 O.sub.3 vapor is allowed to deposit on a surface without the influence of the laser emission. This method is used for surface enhancement of optical lenses.
German Published Application No. 26 00 690 discloses how micro-engravings can be produced in arbitrary materials with laser emission. A reflecting surface layer that has recesses at the locations where the erosive effect is to occur is used in combination with erosive material processing on the basis of laser emission.
However, difficulties have since occurred in conjunction with the employment of this laser-induced deposition from the vapor phase. The method can only be used for substrate materials that absorb the incident laser light to an adequate degree. When substrates have adequate absorption and also high reflection, small differences in the surface quality can lead to relatively greater differences with respect to the absorbed laser power. This leads to great modifications or, respectively, tolerances in the lateral dimensions of the micro-structures produced with the laser beam.
Additionally, local differences in the optical or thermic properties of the substrate surface in non-homogenous materials (ceramics, composites, etc.) or in materials that are partially coated, for example silicon wafers that are partially coated with SiO.sub.2, can lead to great modifications in the lateral and axial (layer thickness) dimensions.